I have a 396/375 in a 67 ss. Front brakes are disc/rear drums. I have an 8" dual diphram booster. Because of the cam, I only get 5-6 inches of vacuum at an idle. I have a cadillac assist vac. pump now, but it originally only pulled down to 10 inches, so I rewired it and installed a vac. switch to operate it. When it gets to vacuum(20 inches according to my vac. gauge) it starts a machine gun sound for a munute or so. This has led to burnt up relays and one fried pump so far. Are there any QUIET VERSION pumps available? Had one from Sumitt but you could hear it a block away. Had to go with the smaller booster due to large valve covers for the roller rockers. I have no vac. leaks, I think the machine gun effect is because the cad. pump is not meant to draw that much vacuum. It was only produced to assist high altitude cold starts, but the pump is compact and fairly quiet.

Ya could just go with manual disc and do away with booster

I've heard that volvo boosters are quite - could use some usefull input on this whole thing.

I switched to a master manual cylinder from a "69 vette in my big block elco and it is sweet, I love it. I tossed the combo valve, ran new lines with a wilwood adjustable proprtioning valve for the rear drums and they are awesom. You can actually feel the brakes its not numb anymore. Plus you have way more room it looks cleaner and its a cheap fix. You just need a manual brake push rod, move it into the top hole in the pedal and the master will bolt right up.

Josh, if I am understanding you, I can still have disc in front but don't need the booster? And I have to get a different proportioning valve?